1. Field of the Invention (Technical Field)
The present invention relates to apparatuses and methods for protecting high-temperature batteries from extreme thermal excursions.
2. Background Art
A major problem with high temperature batteries is that they are prone when failing to extreme thermal excursions and resulting catastrophic failure and fire. In large batteries, this can be triggered by short circuit failures of individual cells. As successive cells develop shorts, circulating currents increase in the battery, driving temperatures above normal operating levels. At some point, a cascade effect can develop where the increasing temperature causes more cells to fail. Placing thermal fuses in the battery at the string or bank level can eliminate thermal runaway by opening the affected electrical circuit before the temperature rises high enough to damage cells in adjacent strings. Although some capacity may be lost, the battery does not undergo a thermal meltdown.
Existing thermal cutoff devices are used to protect equipment such as electric motors from overheating. However, these typically operate at temperatures well below the normal operating temperature of a sodium/sulfur battery (350-400.degree. C.) and cannot be modified to survive this higher temperature environment. The highest rated opening temperature known to Applicants for such a device is 240.degree. C. A device which arguably could perform a fusing function at temperatures above 400.degree. C. is the Babcock BR211 fuse switch. However, this switch is a mechanical switch that is activated by a current pulse. It is much more complex than the thermal fuse of the invention and substantially more costly.